Electron microscope equipment is often required to examine and perform manipulation of micro- and nano-scale objects. In general, electron microscopes employ a beam of electrons to irradiate a sample under study, wherein the wavelength of the electron beam is much smaller than the wavelength of light used in optical microscopes. Modern electron microscopes can view details at the atomic level with sub-nanometer resolution (e.g., 0.1 nm resolution) at a magnification of up to about one million. Electron microscopes and others which may be similarly employed include atomic force microscopes, scanning probe microscopes, scanning tunneling microscopes, near field optical scanning microscopes and transmission electron microscopes, among others.
A scanning electron microscope (SEM) is another type of electron microscope. In an exemplary SEM, a beam of electrons is focused to a point and scanned over the surface of the specimen. Detectors collect the backscattered and secondary electrons reflected or otherwise originating from the surface and convert them into a signal that is used to produce a realistic, three-dimensional image of the specimen. During the scanning process, the detector receives fewer electrons from depressions in the surface, and therefore lower areas of the surface appear darker in the resulting image. SEMs can provide a magnification of up to about two hundred thousand, possibly higher.
A focused ion beam (FIB) system is similar to a scanning electron microscope, except that instead of employing an electron beam, a beam of ions is scanned across the sample. The ion beam is ejected from a liquid metal ion source (e.g., gallium) with a spot size that is usually less than about 10 nm. FIB techniques can be employed in the preparation of samples for subsequent examination by a TEM or other electron microscope.
FIB specimens prepared for TEM are often manufactured by the “lift-out” method to provide a rapid means of preparing an electron transparent cross-section from a specific site of interest. In the lift-out method, a relatively large bulk sample can be inserted into the FIB chamber such that a specimen can be created from the surface of the sample. The specimen is then “lifted out” by the use of an electrostatic probe, which retrieves the sample from its trench and deposits the sample on an examination grid.
However, it can be difficult to accurately position and/or orient the retrieved sample with the electrostatic probe. For example, because the sample is temporarily adhered to the probe merely by electrostatic forces, the sample is not positively secured and may dislodge and/or become contaminated or destroyed. Consequently, an examination grid to which the sample is adhered or welded may be required. Such processes permit examination of the sample in only a single orientation, possibly requiring examination of multiple samples to adequately examine a substrate or substrate region.